1. Field of the Invention
This invention relates to a motor slurry or transfer pump and more particularly to a submersible canned motor transfer pump which transfers high-level radioactive liquid waste or sludge out of a waste tank.
2. Background of Information
Motor transfer pumps are used to transfer high-level radioactive liquid waste out of a waste tank which is approximately 50 to 60 feet deep and which has a diameter ranging from about 75 to about 85 feet with liquid capacities of approximately one million gallons. The liquid waste in the tank is mobilized by a motor mixer pump which agitates the liquid waste so that it is pumpable through the transfer pump. The liquid waste is pumped out of the tank by a transfer pump and may be transferred to another tank or the liquid may be separated from the solid radioactive waste which is vitrified and collected and sealed in containers which are generally buried in underground concrete vaults.
Presently, transfer pumps have an air cooled motor supported on a riser located at the top of the waste tank. The riser has about a 12 inch opening and a mounting flange on the riser suspends a line shaft through the opening and which line shaft must hang down into the tank for an insertion length of up to about 58 feet into the liquid waste in the tank for purposes of emptying the liquid waste out of the tank. The environment in which the transfer pump operates is extremely abrasive and hostile in that the radiation exposure to the components of the transfer pump is up to 300 megarads of gamma radiation. This radioactive liquid waste has a pH greater than 9.0; an absolute viscosity of 1.0 to 50.0 Cp; a specific gravity of about 1.0 to 1.7; a temperature of about 90.degree. C.; and a relative humidity of up to about 100%. In addition, this liquid waste consists mainly of insoluble oxides and hydroxides of aluminum, iron, manganese, and zirconium in mixtures with water up to 50% solids by volume. These solid particles may have a diameter up to 0.040 inches.
These present-day transfer pumps with an air cooled motor driving a line shaft from outside the waste tank employs a column which houses the line shaft in the tank and is filled with pressurized water. At least 5 or more sets of bearings are mounted on the lineshaft to support the radial loads imposed on the long lineshaft, and the pressurized water in the column is used to lubricate the bearings. Mechanical seals are needed at the top and the bottom of the lineshaft to prevent the pressurized liquid in the column from escaping into the tank and to prevent the liquid waste in the tank from entering the column. Additionally, the column is comprised of several pipe pieces with flanges which are joined together requiring gaskets or seals, and the lineshaft consists of several shaft pieces coupled at about 10 ft. intervals. The bearings are located at the column pipe joints.
This present design for a transfer pump has several disadvantages; one being that it experiences a very short life in that it operates only for about 100 hours before it needs to be repaired or replaced. Another disadvantage is that the pressurized water in the column for lubricating the bearings leaks out of the column and into the contaminated liquid in the waste tank which adds to the amount of contaminated liquid which must be pumped out of the tank and processed. A further disadvantage is that the long lineshaft has poor rotor dynamic performance. With a multiple bearing system such as that in the present-day transfer pump, if wear occurs at one bearing, shaft vibration will increase greatly. Alignment of a multiple bearing system is difficult. One or two bearings are always highly loaded and prone to wear and/or failure. The transfer pump has seals which must be maintained. The seals are rubbing face seals which wear with time, particularly, if abrasive particles are present. These seals must either be replaced which is difficult to do with a radioactive pump or the pump must be disposed of if the seals leak too much.
"Canned" motors are well-known in the art and are disclosed or discussed in U.S. Pat. Nos. 5,101,128; 5,185,545; 5,220,231, and 5,252,875 which relate to submersible motor propulsor units.
Thus, there remains a need for a transfer pump used for transferring high-level radioactive liquid waste in a waste tank which has a longer mechanical and electrical life expectancy than current designs for a transfer pump.
There remains a further need for a transfer pump used in the environment discussed hereinabove which has a longer life in that it has an improved dynamic performance compared to present-day transfer pumps and does not require seals to prevent liquid from escaping out of or seeping into the long column which houses the lineshaft.